Inhaled Remimazolam Potentiates Inhaled Remifentanil in Rodents

Remimazolam is an ester-based short-acting benzodiazepine currently in clinical trials for IV administration. This study explored the feasibility of delivering remimazolam alone and as an adjunct to remifentanil via inhalation in rodent models.

Mice were exposed to remimazolam via inhalation; sedation was assessed using time to movement outside a set perimeter. Rats were also exposed to remimazolam aerosol alone and in combination with inhaled remifentanil, and analgesia was quantified by using a tail flick meter. Pulmonary injury was assessed in mice using mechanics measurements.

Mice showed significantly increased time to movement outside a set perimeter after 5-minute exposure to increasing concentrations (10-25 mg/mL solutions) of inhaled remimazolam aerosols. Differences in mean (95% confidence interval) time to movement from pretest baseline group (0.05 [0.01-0.09] minutes) were 11 (4-18), 15 (5-26), 30 (19-41), and 109 (103-115) minutes after exposure to remimazolam aerosol of 10, 15, 20, and 25 mg/mL, respectively (P = .007 - P < .0001). Exposure of rats to remimazolam aerosols alone failed to produce sedation or analgesia after a 5-minute exposure. When remimazolam (10 or 25 mg/mL) was administered in combination with 250 μg/mL remifentanil, there was a significant difference in time to tail flick (P < .0001) consistent with a strong analgesic effect. Mean (95% confidence interval) differences in time to tail flick from the pretest baseline group (3.2 [2.5-3.9] seconds) were 14 (10-18) seconds when 250 μg/mL remifentanil was administered with either 10 or 25 mg/mL remimazolam. Remimazolam alone or in combination with remifentanil did not cause lung irritation, bronchospasm, or other adverse pulmonary events to the respiratory tract of mice as assessed by Flexi-Vent pulmonary function tests.

Remimazolam can significantly potentiate the analgesic effect of remifentanil when concurrently delivered via inhalation.